This project systematically compares the effects of drugs on the predatory behavior of rats, cats, grasshopper mice, ferrets, hamsters, and other selected species. In general, drugs are chosen for study with other species after initial findings that show they affect mouse killing by rats, because more information is available about drug effects on that type of predatory behavior than any other. Drugs that block mouse killing by spontaneously predatory rats (e.g., d-amphetamine), and those that initiate mouse killing by spontaneously non-killing rats (e.g., chlordiazepoxide) are of equal interest to this project. Studies are carried out with various prey (e.g., insects, amphibia, small mammals). Analyses of the mechanisms of action of active drugs, involving manipulations of relevant brain and hormonal target sites (e.g., amygdala, adrenal glands) are pursued when such studies are indicated.